Thought I'd jump on this post and plead for some assistance

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My instrument cluster is playing up. It doesn't always light up when I start the car, problem seems to manifest if I leave it standing for plenty of hours, but not over a shorter period. Up until now it has always sprung into life within the first 60 seconds or so (usually nearer 15-30 secs), assuming it doesn't just start normally from the off. I can hear a ticking sound until it starts and occasionally the illumination 'pulses' alongside the ticking. There is no visible Time/Date or mileage. None of the gauges work nor warning lights etc.
Once it comes on everything is normal all the warning lights do what I'd expect, gauges also work fine. If I switch car off and back on everything is normal from the off (or has been so far).
Anyway car is in with a local independent haemorrhaging cash

and I got a call earlier to say this particular problem is with the cluster and it needs replacing.
Anyone any experience of swapping them over. I can see units on Ebay at variable costs.... are they plug and play (Tdi to Tdi). What happens with the mileometer. Any help or advice would be appreciated.